1. Field
Embodiments of the disclosure relate generally to the field of handling of semiconductor wafers for processing or testing and more particularly incorporate a chuck with a vacuum ring that can be vacuum adhered to the underside of a top plate for required operations and then released to a motion stage for repositioning.
2. Background
Handling and measuring of semiconductor wafers is accomplished by a class of tools known in the semiconductor fabrication industry. Such tools ordinarily have a chuck for holding the wafer, a motion stage to translate the wafer in x, y, z directions, and angularly rotate (referred to as theta rotation), and a supporting frame to hold a measurement instrument over the wafer. The measurement instruments can be optical as in the case of optical inspection equipment, acoustic, mechanical such as profilometers or scanned probe microscopes, or electrical as in the case of probers.
In each of these cases, it is critical to be able to move the wafer from location to location under the instrument. In most cases, the motion of the mechanical stage is difficult to stop in a precise and complete way. In the case of mechanical bearings common to each machine, the bearing will have some settling time and error associated with its motion. Furthermore, the larger the motion range, the greater will be the errors and settling time. Mechanical vibration also follows the same principle where the greater the motion range, the larger the vibration. Additionally, vibration has a spectral component where the larger the structure, the lower the frequency of vibration. Typically, lower frequency vibrations are worse because they are within the measurement frequency band and also have higher amplitudes sometimes referred to as ‘pink’ noise.
Probing or measuring instruments that work on wafers are plagued with vibration noise, settling time and drift during use on very small features present on the wafer. The instrument mounted to the frame of the tool is used to measure some small feature on a wafer but is suspended via a large mechanical loop and therefore is susceptible to these factors. In the case of a wafer measuring instrument, the thermally induced drift can be dominated by any sort of temperature instability. The frame and motion stage of the tool required to measure all parts of the wafer is somewhat more than twice size of the geometry being measured so that for a 300 mm wafer common in use today, the frame structure is typically on the order of 800 mm across, for the new 450 mm standard wafer, the frame will be more than 1000 mm. If the frame is made from steel components, the thermal expansion due to a 1 degree variation can be 800 mm times the coefficient of thermal expansion or 6 parts per million per degree or about 5 um per degree. Many measurements require sub micron accuracy and therefore, a large mechanical loop is highly undesirable.
It is therefore desirable to provide a system for suspending a measurement instrument and wafer holding fixture to uncouple from the mass and undesirable characteristic features of the larger tool while maintaining the ability to employ the mechanical systems of the tool for coarse position movement of the wafer.